The present invention relates generally to networking. More specifically, a method and apparatus for distributed Network Address Translation is disclosed.
As the IP protocol has continued to be in widespread use, a plethora of network service appliances have evolved for the purpose of providing certain network services not included in the protocol and therefore not provided by standard IP routers. Such services include NAT, statistics gathering, load balancing, proxying, intrusion detection, and numerous other security services. In general, such service appliances must be inserted in a network at a physical location where the appliance will intercept all flows of interest for the purpose of making its service available.
FIG. 1 is a block diagram illustrating a prior art system for providing a network service. A group of clients 101, 102, and 103 are connected by a network 110 to a group of servers 121, 122, 123, and 124. A network service appliance 130 is physically located in the path between the clients and the servers. Network service appliance 130 provides a service by filtering packets, sending packets to specific destinations, or, in some cases, modifying the contents of packets. An example of such modification would be modifying the packet header by changing the source or destination IP address and the source or destination port number.
Network service appliance 130 provides a network service such as load balancing, caching, or security services. In providing security services, network service appliance 130 may function as a proxy, a firewall, or an intrusion detection device. For purposes of this specification, a network service appliance that acts as a load balancer will be described in detail. It should be noted that the architecture and methods described are equally applicable to a network service appliance that is functioning as one of the other above described devices.
Network service appliance 130 is physically located between the group of servers and the clients that they serve. There are several disadvantages to this arrangement. First, it is difficult to add additional network service appliances when the first network service appliance becomes overloaded because the physical connections of the network must be rerouted. Likewise, it is difficult to replace the network service appliance with a back up network service appliance when it fails. Since all packets pass through the network service appliance on the way to the servers, the failure of the network service appliance may prevent any packets from reaching the servers and any packets from being sent by the servers. Such a single point of failure is undesirable. Furthermore, as networks and internetworks have become increasingly complex, multiple services may be required for a single network and inserting a large number of network service appliances into a network in places where they can intercept all relevant packet flows may be impractical.
The servers may also be referred to as hosts and the group of servers may also be referred to as a cluster of hosts. If the group of servers has a common IP address, that IP address may be referred to as a virtual IP address (VIPA) or a cluster address. Also, it should be noted that the terms client and server are used herein in a general sense to refer to devices that generally request information or services (clients) and devices that generally provide services or information (servers). In each example given it should be noted that the roles of client and server may be reversed if desired for a particular application.
A system that addresses the scalability issues that are faced by network service appliances (load balancers, firewalls, etc.) is needed. It would be useful to distribute functions that are traditionally performed by a single network element and so that as much function as possible can be performed by multiple network elements. A method of coordinating work between the distributed functions with a minimum of overhead is needed.
Although network service appliances have facilitated the development of scalable server architectures, the problem of scaling network service appliances themselves and distributing their functionality across multiple platforms has been largely ignored. Network service appliances traditionally have been implemented on a single platform that must be physically located at a specific point in the network for its service to be provided.
For example, clustering of servers has been practiced in this manner. Clustering has achieved scalability for servers. Traditional multiprocessor systems have relatively low scalability limits due to contention for shared memory and I/O. Clustered machines, on the other hand, can scale farther in that the workload for any particular user is bound to a particular machine and far less sharing is needed. Clustering has also facilitated non-disruptive growth. When workloads grow beyond the capacity of a single machine, the traditional approach is to replace it with a larger machine or, if possible, add additional processors within the machine. In either case, this requires downtime for the entire machine. With clustering, machines can be added to the cluster without disrupting work that is executing on the other machines. When the new machine comes online, new work can start to migrate to that machine, thus reducing the load on the pre-existing machines.
Clustering has also provided load balancing among servers. Spreading users across multiple independent systems can result in wasted capacity on some systems while others are overloaded. By employing load balancing within a cluster of systems the users are spread to available systems based on the load on each system. Clustering also has been used to enable systems to be continuously available. Individual application instances or machines can fail (or be taken down for maintenance) without shutting down service to end-users. Users on the failed system reconnect and should not be aware that they are using an alternate image. Users on the other systems are completely unaffected except for the additional load caused by services provided to some portion of the users that were formerly on the failed system.
In order to take full advantage of these features, the network access must likewise be scalable and highly available. Network service appliances (load-balancing appliances being one such example) must be able to function without introducing their own scaling limitations that would restrict the throughput of the cluster. A new method of providing network services using a distributed architecture is needed to achieve this.
It would be useful if network address translation (NAT) could be implemented using a distributed architecture without the need to place NAT machines in a position to intercept all packets that are selected to undergo NAT. It would be especially useful if a service manager could be used to determine certain addresses to be translated using NAT and also certain ports to be translated. Once a determination is made by such a service manager, it would be useful if a forwarding agent could be used to carry out the NAT without requiring the service manager to handle every packet that undergoes NAT.
A system and method for performing network address translation using a service manager and a forwarding agent is disclosed. The service manager sends a wildcard affinity to the forwarding agent that attracts packets having a protocol, a source address, destination address, source port or a destination port that is to be translated. When the forwarding agent receives a packet that matches a wildcard affinity stored by the forwarding agent, the forwarding agent sends the packet to the service manager. The service manager determines what address and port translations, if any should be performed on that packet and related packets. The service manager then sends instructions to the forwarding agent for handling such packets.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. Several inventive embodiments of the present invention are described below.
In one embodiment, a method of specifying network address translation for a set of packets includes sending a first set of instructions to a forwarding agent specifying criteria for designated packets that are designated to undergo network address translation. A matching packet is received from the forwarding agent that matches the specified criteria. A network address translation scheme is determined for the matching packet. A second set of instructions are sent specifying the network address translation scheme for packets associated with the matching packet.
In one embodiment, a service manager configured to specify network address translation for a set of packets to a forwarding agent includes a forwarding agent sending interface configured to send a first set of instructions to the forwarding agent specifying criteria for designated packets that are designated to undergo network address translation. A forwarding agent receiving interface is configured to receive from the forwarding agent a matching packet that matches the specified criteria. A processor is configured to determine a network address translation scheme for the matching packet. The forwarding agent sending interface is further configured to send a second set of instructions specifying a network address translation scheme for packets associated with the matching packet.
In one embodiment, a method of performing network address translation based on instructions received from a service manager includes receiving a first set of instructions from a service manager specifying criteria for designated packets that are designated to undergo network address translation. A matching packet that matches the specified criteria is sent to the service manager. A second set of instructions is received that specifies the network address translation scheme for packets associated with the matching packet. A packet associated with the matching packet is received and network address translation is performed according to the network address translation scheme on the packet associated with the matching packet.
In one embodiment, a forwarding agent configured to perform network address translation based on instructions received from a service manager includes an instruction receiving interface configured to receive a first set of instructions from a service manager specifying criteria for designated packets that are designated to undergo network address translation. A sending interface is configured to send to the service manager a matching packet that matches the specified criteria. The instruction receiving interface is further configured to receive a second set of instructions specifying the network address translation scheme for packets associated with the matching packet. A packet receiving interface is configured to receive a packet associated with the matching packet. A processor is configured to perform network address translation according to the network address translation scheme on the packet associated with the matching packet.
These and other features and advantages of the present invention will be presented in more detail in the following detailed description and the accompanying figures which illustrate by way of example the principles of the invention.